From Creatures Wikia
The term is used within the game and genetics editor to denote the fourth species slot in the later Creatures game engines (Creatures 3 and Docking Station), unused by an existing ingame species. Another good example of the use of the Geat sprite slot is in making sprite sets for other already defined breeds after all of the other breed slots are taken. Lis Morris's Gaia for Creatures 3 is a good example: it is a creature that didn't fit under the typical creature divisions. The slot wasn't widely used in development until Creatures 3, and was referred to in Creatures 1 and Creatures 2 by a different name (Shee).
In Norse mythology, Geatland is another name for Gotland, which is now in Sweden. The Geats were the Scandinavian inhabitants of that island. According to Jordanes and modern archaeological finds, Geats are, in reality, the same as the Goths. Beowulf, who defeated Grendel in a bloody battle, was a prince of the Geats.